Controller and driver communication for switching regulators

ABSTRACT

Pulse width modulation (PWM) controllers and output stage driver circuits and related methods of communicating switching regulator mode information. The controller includes circuitry that recognizes intervals when the load driven by the regulator is in a low power mode. Responsive to recognizing the low power mode, the controller generates a PWM mode signal having at least three (3) different levels including at least one intermediate level that is coupled to at least one driver. Based on the PWM mode signal, the regulator is switched into a power saving low power operational mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 12/840,466filed on Jul. 21, 2010, which is a divisional of U.S. application Ser.No. 11/935,535, filed on Nov. 6, 2007, now U.S. Pat. No. 7,782,035,which claims priority to U.S. Provisional Application No. 60/908,539,filed on Mar. 28, 2007, all of which are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

It is known to improve synchronous switching voltage regulatorefficiency at light load conditions to have the regulator operate underdiode emulation mode (DEM). With DEM enabled, the bottom-side MOSFETswitch is disabled preventing negative current flow from the outputinductor during low load operation. Under heavy loads, the voltageregulator operates under forced continuous conduction mode (FCCM). InFCCM, the controller always operates as a synchronous rectifier,switching the bottom-side MOSFET regardless of the output load. Thus, inFCCM, the inductor current flows in both directions.

FIG. 1 is a block diagram schematic showing a conventional pulse widthmodulation (PWM) controller and driver arrangement 100 showingconventional signaling to implement the diode emulation communicationbetween a controller 110 and drivers 120 and 130, for a two-phaseregulator system. The arrangement 100 uses dedicated FCCM pins. Driver120 drives one phase and driver 130 drives the other phase.Specifically, controller 110 has an FCCM pin where an FCCM signal isprovided and drivers 120 and 130 each have an FCCM pin for receiving theFCCM signal. Drivers 120 and 130 are each associated with respectivephases. In a common embodiment, drivers 120 and 130 drive synchronousoutput switches coupled to an inductor which is connected to a load,such as a microprocessor. When the load is a microprocessor, themicroprocessor generally provides a mode indicating signal generallyreferred to as a mode select signal which can be used as an externaltriggering signal to trigger the regulator to enter DEM.

The mode select signal is generally in one of two states indicative ofthe level of the load current drawn. For example, when themicroprocessor senses the load current being heavy, the mode select canbe in the “1” state. When the microprocessor senses the load currentbeing light, such as below a predetermined current threshold set on themicroprocessor, the mode select output can be in the “0” state. ForINTEL™ microprocessors, the mode select signal is referred to as aProcessor Power Status Indicator (PSI# signal).

While the mode select signal asserted is low, the FCCM pin of controller110 will send a low FCCM signal to initiate the drivers 120 and 130 intoDEM to save power and improve light load efficiency. However, duringsignificant output over voltage events, even if PSI# is asserted low,the controller 110 sends a high FCCM signal to turn on the low-side FETswitch and sink current to protect the processor or other load from overvoltage stress. This requires routing the FCCM signal to all drivers inmultiphase arrangements. In the case the controller and gate drivers areon separate chips, as the number of phases increases, the PCB layoutbecomes complex and traces becomes crowded in a typical spacing limitedmotherboard. Moreover, some new controllers and gate drivers have lowpin counts (e.g., 8 pins). As a result, there may be no controller orgate driver pin available for accommodation of an FCCM signal.

FIG. 2 is a simulated conventional diode emulation communication timingdiagram 200 for one of the two phases controlled by signalingarrangement 100 shown in FIG. 1. The UGATE and LGATE signals areprovided by gate drivers 120 and 130, which as known in the art, arecoupled to upper and lower gates of synchronous output switches,respectively. The UGATE and LGATE signals are responsive to the FCCM andPWM signals provided by controller 110. Note the presence of a dedicatedFCCM signal and the conventional two (2) state PWM signal used.

At time to, FCCM becomes low. In response, DEM mode is soon enabled,preventing negative current flow from the output inductor (I_(L)) asshown between times t₁ and t₂ and times t₃ and t₄ in FIG. 2. A dedicatedFCCM pin and the required signaling to implement DEM increases the pincount for both the controller and the driver as well as the layoutcomplexity. What is needed is a simplified DEM communication method thateliminates the need for the presently required extra FCCM pin for thecontroller and the FCCM pin for the driver(s).

BRIEF DESCRIPTION OF THE DRAWINGS

A fuller understanding of the present invention and the features andbenefits thereof will be accomplished upon review of the followingdetailed description together with the accompanying drawings, in which:

FIG. 1 is a block diagram schematic showing a conventional signalingarrangement to implement diode emulation communication.

FIG. 2 is a simulated conventional diode communication timing diagram.

FIG. 3 is a simplified block diagram showing a regulator including acontroller/gate driver signaling arrangement according to an embodimentof the invention.

FIG. 4( a) is a block diagram of a system including an exemplarytwo-phase non-coupled inductor regulator, according to an embodiment ofthe invention.

FIG. 4( b) provides waveforms including an exemplary PWM mode signalgenerated by the controller shown in FIG. 4( a) along with resultinginductor currents for the respective phases.

FIG. 5( a) is a block diagram of a system including an exemplarytwo-phase coupled inductor (CI) regulator, according to an embodiment ofthe invention.

FIG. 5( b) provides exemplary signals including PWM mode signalsgenerated by the controller shown in FIG. 5( a) along with resultinginductor currents for the respective phases.

FIG. 6 is a simplified schematic for a multiphase PWM controlleraccording to an embodiment the invention.

FIG. 7 is a simplified schematic for an exemplary driver operable todetect a PWM mode signal according to an embodiment of the invention.

FIG. 8 is a timing diagram showing signals including an exemplary PWMmode signal for a two (2) phase-coupled inductor case with both phasesremaining on in DEM, according to an embodiment of the invention.

FIG. 9 is a timing diagram showing signals including an exemplary PWMmode signal shown implementing diode braking, according to an embodimentof the invention.

FIG. 10 is a block diagram of a system comprising a multi-phasenon-coupled regulator, according to an embodiment of the presentinvention.

FIG. 11 is a block diagram of a system comprising a multi-phase coupledinductor regulator, according to another embodiment of the presentinvention.

SUMMARY

According to one embodiment of the invention, a method of communicatingmode information for operation of a switching regulator between a PWMcontroller and at least one output stage driver is provided. The driveris coupled to at least one output switch which drives a load. A modeindicating signal is received at the controller, wherein the modeindicating signal is operable to indicate intervals of time when theload is in a low power mode. Based on the mode indicating signal, it isdetermined when the load is in the low power mode. Responsive to thedetermining, the controller generates a PWM signal encoded with modeinformation referred to herein as a PWM mode signal. The PWM mode signalcomprises at least three (3) different levels including at least oneintermediate level. The PWM mode signal is coupled to the input of thedriver. Based on the PWM mode signal, the regulator is switched into atleast one low power operational mode. The low power operational mode cancomprise diode emulation mode (DEM), phase dropping mode and a diodebraking mode.

A transition of the PWM mode signal between a high or low level and theintermediate level can be used for triggering said switching. Forexample, diode braking can be initiated when the PWM mode signaltransitions from the high level to the intermediate level.

The PWM mode signal can comprise a repetitive pattern which begins at atransition from a high level to a low level, reaches the intermediatelevel after a first time, and transitions from the intermediate level tothe high level at a second time, the second time after the first time.

A modulation controller according to an embodiment of the inventioncomprises an error amplifier which receives a reference voltage and anoutput voltage signal from a switching regulator being controlled by thecontroller at its inputs. The controller includes at least onecomparator, a first input of the comparator coupled to an output of theerror amplifier and a second input coupled to receive a ramp signal. Apulse timing circuit having a first input is coupled to an output of thecomparator, and a second input is coupled to receive a mode indicatingsignal, wherein an output of the pulse timing circuit operable toprovide a PWM mode signal having at least three (3) different levelsincluding at least one intermediate level. The controller can comprise amulti-phase controller.

A driver according to an embodiment of the invention for driving outputswitches coupled to a load in a switching regulator-based systemcomprises an input stage comprising a pair of comparators operable toreceive a PWM mode signal having at least three (3) different levelsincluding at least one intermediate level and at least one detectioncircuit operable to detect the PWM mode signal. An output stage iscoupled to receive outputs from the input stage and the detectioncircuit. The output stage is operable for recognizing when the PWM modesignal is at or transitioning to or from the intermediate level toanother level and responsive thereto providing a plurality of outputsignals to the output switches operable to switch the regulator into atleast one low power operational mode.

According to another embodiment of the invention, a modulationcontroller and gate driver combination is described. In yet otherembodiments of the invention, systems including microprocessor-basedsystems are also described.

DETAILED DESCRIPTION

Embodiments of the present invention are more particularly described inthe following description and examples that are intended to beillustrative only since numerous modifications and variations thereinwill be apparent to those of ordinary skill in the art. As used in thespecification and in the claims, the singular form “a,” “an,” and “the”may include plural referents unless the context clearly dictatesotherwise. Also, as used in the specification and in the claims, theterm “comprising” may include the embodiments “consisting of” and“consisting essentially of”.

In various embodiments of the present invention, an improved method andrelated controller and gate driver architecture for communicating modeinformation between a PWM controller and one or more gate drivers isprovided. Methods according to embodiments of the invention compriseproviding a PWM controller having at least one PWM output coupled to aninput of at least one gate driver. The controller is operable forgenerating a PWM mode signal having at least three (3) levels includingat least one intermediate level responsive to the receipt of a modeindicating signal which indicates whether the load is in a low powermode (e.g., PSI# signal), or low current regulator operation. Theinvention is applicable to both single phase and multi-phase regulatorsystems, and both coupled inductor and non-coupled inductorarrangements.

FIG. 3 is a simplified block diagram showing a two-phase regulator 300including a controller/gate driver signaling arrangement according to anembodiment of the invention. Regulator 300 comprises a modulationcontroller 310 coupled to two (2) drivers 310 and 320, showncollectively as controller/driver combination 368. As described below,the controller/driver 368 uses a new PWM mode signal which allows theregulator to enter a low power (power saving) operational mode, such asDEM and/or phase dropping for multiphase systems, without the need for adedicated FCCM signal. Although the invention is described with respectto NMOS output switches, specifically double diffused NMOS switches(n-DMOS), those having ordinary skill in the art will recognize standardsingle diffused and/or PMOS output switches may also be used.Controller/gate driver 368 can be on the same integrated circuit chip368. However, in another embodiment of the invention, the controller 310and one or more gate drivers 320 and 330 can be on separate chips.

The drivers 320 and 330 receive the PWM mode signals, PWM1 and PWM2,generated by controller 310 at one of their inputs. In response to thedrivers 320 and 330 detecting the PWM mode signal being at anintermediate level, such as in one embodiment for at least apredetermined period of time, the gate drivers 320 and 330 provideoutput signals operable to drive the gates of respective output switches325 and 335, respectively, that are shown coupled to inductor 326 and327, so that regulator 300 enters a low power operational mode. The lowpower operational mode can comprise at least one of a diode emulationmode (DEM), phase dropping mode, or diode braking mode.

As used herein, phase dropping refers to removing (shutting down) one ormore coupled phases in a multiphase regulator system. Diode braking asused herein refers to turning off both synchronous output switches(UGATE and LGATE), such as after the PWM mode signal transitions from ahigh level to the intermediate level.

Phase-dropping allows the device to be configured to alternate thenumber of active phases (e.g., 2-phase to 1-phase operation, or 3-phaseto 2-phase operation). Combining the dynamic phase add-drop featuretogether with diode emulation mode at light load can further maximizethe regulator efficiency over a wide load range, which in the case ofbattery power supplies, can significantly improve battery life.

In one embodiment, when the controller 310 receives a mode indicatingsignal, such as a low PSI# signal from a microprocessor, or a currentsense signal (e.g., via a RDSon sensing circuit) indicating low powerregulator operation, controller 310 generates the PWM mode signalaccording to embodiments of the invention. Exemplary PWM mode signalsare shown in FIGS. 4( b) and 5(b) which evidence three (3) differentexemplary states, specifically, ground, VCC/2 and VCC. The PWM modesignal is a pattern that is recognized by the gate drivers 320 and 330and allows drivers 320 and 330 to realize that the microprocessor (orother load) is operating at a low power mode and to enter DEM and/orimplement diode braking or phase dropping. Thus, one embodiment of theinvention includes generation of a PWM mode signal, and recognition ofthe PWM mode signal to trigger low power regulator operational modesincluding one or more of DEM, diode braking and phase dropping.

FIG. 4( a) is a block diagram of a system 400 including an exemplarymulti-phase non-coupled inductor regulator 405 according to anembodiment of the invention. System 400 comprises multi-phase modulationcontroller 310, drivers 320 and 330, and synchronous switches 440 and445 which each drive an inductor, L1 and Lx, respectively. The inductorsare both coupled to load 408. In one exemplary embodiment, load 408 is amicroprocessor and provides a PSI# signal which is coupled to an inputof controller 310. Alternatively, instead of using a PSI# or equivalentmode indicating signal, for example, the signal sensed by the controllercan be via DCR or Rdson sensing.

FIG. 4( b) provides waveforms including an exemplary PWM mode signalgenerated by controller 310 for phase 1 and phase x. Gate driver 320 and330 output waveforms (UG and LG) and the inductor currents (IL) are alsoshown for each phase shown. Responsive to the PSI# signal shown goinglow, at time t₁ PWM1 begins a repetitive PWM mode signal pattern showncomprising a negative going pulse to the low level, holding at the lowlevel for a short time (such as 200 ns), and then at t₂ rising to anintermediate level, and at t₃ rising to the high level.

As seen from IL1, the PWM mode signal PWM1 provided to driver 320results in LG1 staying low which implements DEM as evidenced by the zeroL1 inductor current (0 A) period within the time interval t₂ to t₃ Phasex is shown implementing phase dropping during the PSI# low period attime t₄. At time t₄, a negative going PWMx pulse is shown reaching thelow level, holding at the low level for a short time (such as 200 ns),and then at t₅ rising to the intermediate level. Soon after reaching theintermediate level, phase UGx and LGx (after a brief high period) remainlow to implement phase dropping of phase x as evidenced by ILx=0 Ashortly after t₅.

The phase dropping shown starts at t₄, and in one embodiment phasedropping begins when the highest phase goes to PWM=1 for the last time,then enters DEM, while the remained phase PHASE 1, enters the repetitivepattern. For instance, in a 4-phase fixed frequency case, the sequencecan start from PWM 4, while PWM 1 will enter DEM at a later time.

The repetition rate of the repetitive pattern depends upon thecontroller implementation and V_(COMP) signal (i.e. load). It can be avariable or a fixed frequency control. In the case of a light load case(e.g., 0 to 0.1 A), in one embodiment the pulse can be skipped for fixeda frequency control (e.g., mid-level can be very long, operating inburst mode).

Compared to the conventional PWM signal shown in FIG. 2 which uses aconventional PWM signal that provides only a single high level andsingle low level that is at the single low voltage level (e.g., ground)for the entire low period, the exemplary PWM mode signal according tothe invention provides a three (3) state pattern including anintermediate level. As noted above, the PWM mode signal allows savingthe controller and driver pins required by conventional controllers anddrivers. System performance using controller to driver communicationsaccording to the invention as is generally essentially unchanged ascompared to a regulator system using conventional controller to drivercommunications.

FIG. 5( a) is a block diagram schematic of a system 500 including anexemplary two-phase coupled inductor (CI) regulator 505 comprisingcontroller 310, drivers 320 and 330, synchronous switches 440 and 445,according to an embodiment of the invention. Synchronous switches 440and 445 drive inductors 520 and 521, respectively, which are bothcoupled to microprocessor load 408.

FIG. 5( b) provides exemplary signals for regulator 505 including anexemplary PWM mode signal generated by controller 310 for phase 1 andphase x. Gate driver 320 and 330 output waveforms (UG and LG) and theinductor currents (IL) are also shown for each phase.

While PSI# is low, at time t₁, the repetitive PWM mode signal patternbegins for phase 1. Phase 1 is shown implementing DEM mode. Therepetitive pattern for phase x is seen beginning at t₂. Soon after t₂phase x is dropped. However, ILx is not always at 0 A after beingdropped. Specifically, since the respective phases (phase 1 and phase x)are coupled, in the case of DMOS output switches, the dropped phase(phase x) should have its low-side FET turned on to circulate thecoupled current to avoid high body-diode conduction losses. This can beaccomplished by the gate driver 330 sending the LGx signal shown in FIG.5( b) to switches 445 to turn on the low side DMOS switch (LGATE)whenever the remained phase (phase 1) has its associated high side DMOSswitch turned on.

FIG. 6 is a schematic for PWM controller 310 which is operable toprovide PWM mode signal generation according to an embodiment thepresent invention. Controller 310 includes error amplifier 601 whichprovides an output V_(Comp). Comparator 602 is shown receiving Vcomp atits +input and a ramp oscillator signal at its negative input.Controller 301 includes tri-state/diode braking circuit 603 whichprovides a diode break triggering signal, such as when PWM_H and PWM_L(PWM_H and PWM_L are outputs from AND gates 606 and 607 described below)are at the low level and the circuit sees a high to mid-level transition(e.g., 5V to 2.5V transition). In the diode braking mode, both high-sideand low-side FETs turn off. With the low-side FET off, the positivecurrent goes through the body-diode, which results in a high voltage(V_(OUT)+Vdiode) across the output inductor, yielding a higher inductorcurrent falling rate and lowering the output voltage overshoot in theload release transient.

Controller 310 includes a pulse timing circuit comprising AND gate 606,AND gate 607, OR gate 609, AND gate 610 and AND gate 613. An output ofthe pulse timing circuit is operable to provide a PWM mode signal havingat least three (3) different levels including at least one intermediatelevel.

The output from comparator 602 is shown coupled to one input of AND gate606 and is inverted and coupled to an input of AND gate 607. The outputfrom diode braking circuit 603 is shown coupled to an input of both ANDgates 606 and 607 (shown after inversion).

The PWM_H output of AND gate 606 is coupled to the gate of DMOS switch611. When PWM_H is high, the PWM output 620 of controller 301 goes high.Controller 310 also includes pulse edge generator circuit 608. Theoutput of AND gate 607 (PWM_L) is coupled to an input of pulse edgegenerator circuit 608, which determines how long the PWM=Low during PSI#mode for both the non-coupled and coupled inductor cases. The output ofpulse edge generator circuit 608 and PSI# (or other signal indicative oflow power operation) is coupled to OR gate 609. The output of OR gate609, PWM_L_PSI, and PWM_L (the output of AND gate 607) are coupled torespective inputs of AND gate 610. The output of AND gate 610 is coupledto the gate of DMOS switch 612 and is inverted and coupled to an inputof AND gate 613. The output of AND gate 607 is coupled to the otherinput of AND gate 613. The output of AND gate 613 shown as PWM_Mid iscoupled to the gate of DMOS switch 614. The drain of DMOS switch 614 iscoupled to the PWM output 620 of controller 310. The source of DMOSswitch 614 is coupled to a mid voltage level source, shown as 0.5 VCC(VCC/2). In operation of controller 310, PWM is driven low wheneverPWM_L is high and PSI# is high; PWM is low whenever PWM_L_PSI is highand then driven to a mid level whenever PWM_L_PSI is low (e.g., pulsegenerated by pulse edge generator circuit 608 only passes through togenerate a DEM pattern whenever PSI# is low).

In the case of a coupled inductor, the edge pulser circuit 608 can betriggered by the falling edge of the PWM signal for the other phase.Thus, in the coupled phase case, while in DEM (e.g., PSI#=low), therespective PWM signals shown (PWM1 and PWMx) can stay low until thefalling edge of the other PWM signal, and then enter into a middle level(e.g., ½ VCC) for the rest of the “low” period. This situation isdescribed relative to FIG. 8 which shows exemplary waveforms for thecoupled inductor case as described below.

Controller 310 is indicated as being a multi-phase controller, providingoutputs PWM₁ . . . PWM_(n). The circuitry shown in FIG. 6 can bereplicated for each of the n-phases. Circuitry is generally added tokeep the respective phases from generally turning on at the same time(thus being out-of-phase with one another).

FIG. 7 is a simplified schematic for an exemplary driver 320 which isoperable to interface with PWM controller 310, and provide diodeemulation as well as diode braking, according to an embodiment of thepresent invention. An input of driver 701 is coupled to receive a PWMoutput provided by a controller according to the invention, such as thePWM output 620 provided by controller 310 shown in FIG. 6. PWM modesignal 701 is coupled to inputs of comparators 702 and 703, as well asto inputs to detection circuitry 709. Comparators 702 and 703 are shownas hysteresis providing comparators, which as known in the art, canreduce noise as compared to conventional comparators.

Detection circuitry 709 is operable for detecting certain edgetransitions and to provide signals to other circuitry, including NANDgate 708 and AND gate 727 of output stage 720. Detection circuitry 709comprises an edge detector 704 operable to detect the load entering alow power mode, and an edge detector 706 operable to implement a diodebraking operational mode for the regulator. The inverting input ofcomparators 702 and the non-inverting input of comparator 703 are shownbiased by constant voltage sources, V₁ and V₂, respectively, forexample, V₁=3V and V₂=2V. The output of comparator 703 is coupled toedge blanking circuit 707.

The output of edge blanking circuit 707, edge detector 704 and feedbacksignals from output stage 720 are coupled to inputs of AND gate 708.Driver 320 includes output stage 720 which is operable to provideshoot-through protection, diode emulation, diode braking, and optionalpower-on reset and tri-state during power up/down. Output stage 720 isshown comprising OR gate 710, an output of OR gate 710 coupled one inputof AND gate 711, with the other input of AND gate 711 being the PWM_Hsignal from comparator 702 after inversion by inverter 712. Output stage720 also includes shoot through protection circuitry 725, gates 726 and727, and amplifiers 728 and 729. Output stage 720 receives at its inputsoutputs from comparator 702 (PWM_H), comparator 703 (PWM_L), the outputfrom NAND gate 708, the output from edge detector 706, as well a signalfed back from the PHASE node of the output switches being driven throughcomparator 713. Circuit block 720 provides UGATE and LGATE outputs forcoupling to the upper and low gates of a synchronous output switch (suchas switch 440 shown in FIG. 4( a)).

Regarding the operation of the driver 320 shown in FIG. 7, for DEMoperation whenever the driver 320 driver sees a low to mid-level (e.g.,0 to 2.5V) transition, LGATE will turn off but not until after LGATEturns on for a period of time referred to as a blanking time (e.g., 350ns) and the phase voltage is across “0V” (e.g., 0 A going through thelow-side FET). This 350 ns blanking time is longer than PWM=LOW timegenerated by the controller (e.g., 200 ns) to ensure that the phase nodenoise settles before detecting a zero current across low-side FET(driven by LGATE). For diode braking (DB) operation, whenever the driver320 sees a 5V to 2.5V transition, PWM_H=Low, turning off UGATE, at thesame time, LGATE turns off as well. Other than DE and DB operations, thedriver 320 will generally operate the same manner and have sameshoot-through protection scheme as a standard driver implementation.Combining outputs from edge blanking circuit 707 and edge detector 704and feedback from output stage 720, NAND gate 708 of driver 320effectively generates an internal PSI# signal, thus eliminating the needof dedicated FCCM signal.

FIG. 8 shows exemplary PWM mode signals and the signal at other nodesfor phase 1 and phase x for a multi-phase coupled inductor regulatorsystem (such as system 500 shown in FIG. 5), without phase droppingimplemented. While in DEM (PSI#=low), at time t₁ PWM1 begins the PWMmode signal pattern, while PWMx begins the repetitive signal pattern attime t₂. The respective PWM mode signals (PWM1 and PWMx) are shownstaying low until the falling edge of the other PWM mode signal, andthen enter into a middle level (e.g., ½ VCC) for the rest of the “low”period. For example, at time t₃, the falling edge of PWMx is seen tocoincide with PWM1 reaching the middle level. This arrangement for DMOSswitches ensures that the respective coupled phase lower (LGATE) DMOSswitches switch only once even though the coupled inductor current couldpossibly pass zero amps (0 A) twice at very light load.

In FIG. 9 an exemplary PWM mode signal and the signal at other nodes isshown for a single phase regulator system implementing diodebraking/phase dropping. PSI# (or a low current mode indicating signal)is assumed to be low for the interval shown. At time t₁, the repetitivePWM pattern begins. In the arrangement shown, the transitioning of thePWM mode signal from high to the intermediate level (e.g., ½ VCC) isreserved and triggers the diode braking operation as shown at time t₂.For one exemplary implementation, see, for example, edge detector 706shown in FIG. 7. In the diode braking mode, both the high-side andlow-side FET switches turn off. In the case of DMOS switches, with thelow-side switching FET off, positive current goes through the body-diodeof the LFET, resulting in a high voltage (VOUT+Vdiode) across the outputinductor, yielding a higher inductor current falling rate and loweringthe output voltage overshoot in the load release transient.

Again in the case of DMOS switches, the application of nPhase-coupleddropping to single or 2 (or more) phase operation generally requires alldropped phases to switch their LGATEx (or LGx) to turn on the lower gateto circulate the current and avoid body-diode conduction. As a result,this can add n−1 or n−2 LGATE switching losses and thus reduce some ofthe advantage of improved light load efficiency provided by the presentinvention. One solution is for the n−1 or n−2 phase coupled arrangementis to be operated so that the remained (non-dropped) 1 phase or 2un-coupled or coupled phases use a PWM mode signal, such as the PWM modesignal patterns shown in FIGS. 4( a), 4(b) and 8, to achieve diodeemulation, while other dropped phases (n−1 or n−2) in the case of acoupled core do not carry current and are not required to turn on theirLGATEx in contrast to the nPhase-coupled case described above.

For both coupled and non-coupled cases, to realize low body-diodeconduction stress on both upper and lower DMOS FETs, the dropped phasescan be allowed to be high for the last time before being turned OFF.This makes sure that the corresponding inductors are carrying positive(sourcing) current before entering DEM for a zero current turn off ofLGATEx. This can minimize stress to integrated FETs or discrete FETs. Inthe case phase #1 is the remained phase, in one embodiment the phasedropping sequencing is to start from phase #4. Thus, for a 4-phasesystem, a firing order of 4-1-2-3 can be used to achieve a smoothertransition.

Regarding the controller generation of the PWM mode signal pattern, theslew rate of the PWM mode signal from 0 volts to the intermediatevoltage value (e.g., ½ VCC), or VCC to ½ VCC, should generally belimited because a voltage overshoot/spike can be a dv/dt eventsufficient to cause false triggering. The slew rate should alsogenerally not be too slow to impair dynamic performance. A slew rate of+/− about ½VCC/50 ns is generally a suitable value. Regarding detectionof the PWM mode signal by the gate driver, the driver can detect thelower power mode once seeing the PWM mode signal at the intermediatelevel (e.g., ½ VCC) for more than a predetermined period of time (e.g.,50 ns), which can be configured as a timeout to avoid falsely enteringDEM mode during normal PWM transitions (e.g., 0 to VCC, VCC to 0). Toavoid falsely triggering LGATE OFF too early, the driver can alsoprovide a minimum LGATE on-time, such as 350 ns, to ensure that thephase current is clear before activating the zero amps (0 A) currentsensing circuitries. In addition, the gate driver can use the same PWMmode signal to activate the gate drive voltage drop.

In another embodiment of the invention, when the low power mode signal(e.g., PSI=0) or a low power condition is otherwise detected, anintegrated internal linear regulator that biases the gate drive can beused to change from full rail (e.g., about 12V) to a lower rail (e.g.,about 5V). This embodiment reduces driver switching losses, since thegate drive power losses are proportional to the squared gate drivevoltage.

Finally, to smooth transitions entering and exiting DEM, certainvariations may be used. For example, as known in the art, phasedropping/adding sequencing, re-adjusting the current balance loop, andspecial modulation of compensation output voltage may be used withvarious embodiments of the invention to smooth transitions in and out ofDEM.

As described above, one embodiment of the invention provides modulationcontrollers including multi-phase controllers, and improved drivers. Asnoted above, controllers according to the invention and gate driversaccording to the invention can be combined on the same integratedcircuit to provide integrated an controller/gate driver.

Moreover, as described above, the present invention can be used toprovide improved switching regulators, including both coupled ornon-coupled multi-phase regulators comprising modulation controllers andgate drivers according to the present invention. The improved regulatorscan be used in systems such as servers, desktop computers, graphicscards, notebook computers, telecom switches and routers, which allgenerally include microprocessors, which would generally be the loaddriven by regulator systems based on the invention.

FIG. 10 is a block diagram of a system 1000 that includes a 4-phasenon-coupled regulator 1015 according to an embodiment of the presentinvention which drives one or more microprocessor loads 1005. Asimplified current sensing arrangement is shown for each of the phases.If microprocessor 1005 provides a PSI# signal, the current sensingarrangement shown would not be required for triggering thecommunications between the controller and drivers to implement theregulator entering a low power operational mode. However, as known inthe art, since the microprocessor only provides the low power indication(e.g., PSI#) signal when the system is in a low power mode, the currentsensing signal would still generally be required for current balancebetween the respective phases. Microprocessor load 1005 typicallyprovides processing and supervisory functions for supervised system1010, which can comprise, for example, as noted above, a computersystem, a graphics system, a switch, a router, an embedded system, or ahandheld device.

Regulator 1015 is shown comprising multi-phase (4-phase) controller 1020according to an embodiment of the invention, and drivers 1025, 1030,1035 and 1040. The drivers drive synchronous switches 1040, 1045, 1050and 1055, which are coupled to inductors 1061-1064 respectively, whichdrive microprocessor load 1005.

In typical operation of system 1000, in one embodiment controller 1020receives a mode indication signal from load 1005, wherein the modeindicating signal is operable to indicate intervals of time when theload is a low power mode. Controller 1020 determines when the load is inthe low power mode based on the mode indicating signal. Responsive tothe determining, the controller 1020 generates a PWM mode signalsPWM1-PWM4 which each comprise at least three (3) different levelsincluding at least one intermediate level. The PWM mode signals arecoupled to inputs of drivers 1025, 1030, 1035 and 1040, respectively.Based on said PWM mode signal, the drivers 1025, 1030, 1035 and 1040 areoperable to switch the regulator 1015 into at least one low poweroperational mode.

FIG. 11 is a schematic block diagram of a system 1100 that includes a4-phase coupled inductor regulator 1115 according to an embodiment ofthe present invention which drives one or more microprocessor loads1005. Phases 1 and 3 are coupled to one another, and phases 2 and 4 arecoupled to one another. Thus, in the arrangement shown, the inductors ofphases #1 and 3, shown as reference 1165 and 1167, are coupled, whileinductors of phases #2 and 4, shown as reference 1166 and 1168, are alsocoupled. As with regulator 1015 shown in FIG. 10, regulator 1115 isshown comprising a multi-phase (4-phase) controller 1020 according to anembodiment of the invention, and drivers 1025 (phase #1), 1030 (phase#2), 1035 (phase #3) and 1040 (phase #4). These drivers drivesynchronous switches 1040, 1045, 1050 and 1055, respectively.

System 1100 generally operates in analogously to system 1000 describedabove. However, in system 1100 the inductors of phase 1 and 3 arecoupled, as are the inductors of phase 2 and 4. In the case of lowerpower mode (e.g., PSI#=0) with DMOS output switches, the coupled phasemust to turn on LGATE to circulate coupled current to avoid body diodeconduction while the other phase turns on.

In the preceding description, certain details are set forth inconjunction with the described embodiment of the present invention toprovide a sufficient understanding of the invention. One skilled in theart will appreciate, however, that the invention may be practicedwithout these particular details. Furthermore, one skilled in the artwill appreciate that the example embodiments described above do notlimit the scope of the present invention and will also understand thatvarious modifications, equivalents, and combinations of the disclosedembodiments and components of such embodiments are within the scope ofthe present invention.

Moreover, embodiments including fewer than all the components of any ofthe respective described embodiments may also within the scope of thepresent invention although not expressly described in detail. Finally,the operation of well known components and/or processes has not beenshown or described in detail below to avoid unnecessarily obscuring thepresent invention.

One skilled in the art will understand that even though variousembodiments and advantages of the present invention have been set forthin the foregoing description, the above disclosure is illustrative only,and changes may be made in detail, and yet remain within the broadprinciples of the invention. For example, some of the componentsdescribed above may be implemented using either digital or analogcircuitry, or a combination of both, and also, where appropriate may berealized through software executing on suitable processing circuitry.The present invention is to be limited only by the appended claims.

What is claimed is:
 1. A modulation controller, comprising: an erroramplifier which receives a reference voltage and an output voltagesignal from a switching regulator being controlled by said controller atits inputs; at least one comparator, a first input of said comparatorcoupled to an output of said error amplifier and a second input coupledto receive a ramp signal; and a pulse timing circuit having a firstinput coupled to an output of said comparator, and a second inputcoupled to receive a mode indicating signal, wherein an output of saidpulse timing circuit is operable to provide a pulse width modulation(PWM) mode signal having at least three (3) different levels includingat least one intermediate level.
 2. The controller of claim 1, whereinsaid controller comprises a multi-phase controller.
 3. The controller ofclaim 1, wherein said PWM mode signal comprises a repetitive patternwhich begins at a transition from a high level to a low level, reachessaid intermediate level after a first time, and transitions from saidintermediate level to said high level at a second time, said second timeafter said first time.
 4. The controller of claim 1, wherein one of saidthree (3) levels is a low level, the controller further comprising apulse edge generator circuit coupled to receive said low level and an ORgate, wherein an output of said pulse edge generator circuit and a lowpower mode signal are coupled to said OR gate.